Propylene polymers of relatively high crystallinity are notoriously difficult to dye and considerable research has been carried out for many years to improve the affinity of such polymers to dyestuffs. Generally, the dyeability has been improved by modifying the propylene polymer either by the mechanical addition of a dye receptive compound to the propylene polymer or by the chemical reaction of dye receptors with the propylene polymer yielding dye receptive sites.
Specifically, it has been suggested to mix maleic anhydride with propylene polymer to provide the composition with polar groups being receptive to basic dyes. A serious drawback, however, is that the maleic anhydride is not sufficiently compatible with the propylene polymer and hence produces non-uniform dye receptive sites.
It has also been suggested to graft the propylene polymer with maleic anhydride monomer. However, the grafting reaction is very difficult to carry out and results in a non-homogeneous product of inferior as well as varying mechanical properties, and which cannot be dyed evenly.
According to U.S. Pat. No. 3,765,829 the aforementioned difficulties are said to be overcome with a composition obtained by mixing a polyolefin such as polyethylene or polypropylene with a statistical copolymer of ethylene and maleic anhydride containing between 4 and 15 percent by weight of anhydride groups. The copolymers have a crystallinity and mechanical properties similar to those of ethylene homopolymers prepared by high pressure polymerization and are compatible with the polyolefin base resin provided that the copolymer contain no more than 15 percent by weight maleic anhydride groups. A drawback of using this copolymer with propylene polymer is that a relatively large proportion of the copolymer must be included in the mixture in order to incorporate sufficient maleic anhydride groups to obtain acceptable dyeability of the resultant composition, and this relatively large proportion has the effect of significantly affecting the physical properties of the composition as compared to the propylene polymer by itself.
It is therefore an object of the present invention to provide a propylene polymer composition which is receptive to basic dyes. It is another object of the invention to provide a dyeable propylene polymer composition which requires a lesser proportion of a maleic anhydride polymer than previously required in the prior art. Other objects of the invention will be apparent from the following description.